What do sleeping bag temperature ratings mean?

The EN 13537 rating provides a means of comparing sleeping bags for warmth. Most companies use it or an equivalent test. It should only be used as a guide, however. It doesn’t mean you will be warm at the lowest temperature.

EN 13537 gives four ratings for a sleeping bag:

UPPER COMFORT LIMIT The highest temperature at which a “standard man” weighing 70kg should feel comfortable.

COMFORT The lower limit at which a “standard woman” weighing 60kg in a relaxed posture such as lying on the back should be comfortable.

LOWER COMFORT LIMIT The lower limit at which a “standard man” weighing 70kg in a rolledup body position should be comfortable.

EXTREME TEMPERATURE

The temperature where a “standard woman” will feel very cold and there is a risk of frostbite or hypothermia.

These ratings are calculated using a mannequin with 15 heating zones and temperature zones. The mannequin is dressed in a thermal long-sleeved top and leggings plus long socks, and is placed in the sleeping bag on a mattress.

The key ratings are the Comfort and Lower Comfort ones as these give an idea of the lowest range of temperatures for comfort in a bag.

Most people are likely to feel too cold for comfort long before the Extreme temperature is reached. I’d take the last as meaning that the bag is unsuitable for this temperature. Indeed, I think the Extreme rating is potentially so misleading that it should be scrapped.